Great star coral (Montastraea cavernosa)

The great star coral is classified as Vulnerable (VU) on the IUCN Red List (1) and is listed on Appendix II of CITES (3).

The great star coral grows in fairly small colonies, often forming domes, boulders or cone-shaped structures, or sometimes growing in flat plates or thick crusts (2) (4). Distinctive because of its highly variable appearance, the great star coral may be green, brown, grey, orange or red in colour, while the corallites (hard, calcareous skeletons secreted by individual polyps) are usually large and protruding, varying extensively in shape and size, with 48 alternating, long and short septa radiating from the inside (4) (5).

The great star coral is found in the Caribbean, the Gulf of Mexico, Florida, the Bahamas, and Bermuda (1).

Widely distributed throughout most reef environments, the great star coral is most abundant at depths of between 10 and 30 metres, although some colonies have been observed as deep as 110 metres. The great star coral is more tolerant of turbid and silty environments than most coral species (1) (4).

Colonies of the great star coral possess ‘sweeper tentacles’, elongate tentacles with specialised cnidae (stinging cells), which are distributed on the surface of the colony. The great star coral is unusual in that these sweeper tentacles are usually present at all times on the colony, whereas most other coral species only develop these tentacles in direct response to attacks from neighbouring corals (6). The great star coral is ‘gonochoric’, meaning that colonies are composed entirely of a single sex. Depending on whether the individuals in a colony are male or female, the great star coral will release either eggs or sperm during a mass spawning period between July and October, around seven to eight days after the full moon (7) (8) (9).

Like other reef-building corals, the great star coral has many microscopic, photosyntheticalgae, called zooxanthellae, living within the polyp tissues. The coral and the algae have a mutually beneficial relationship; the coral provides protection for the algae, which in return provide energy and nutrients for the coral through photosynthesis. Both the great star coral and its zooxanthellae are very sensitive to changes in water temperature and acidity, and any increase in the water temperature greater than one or two degrees above the normal average can stress the coral and cause ‘bleaching’, a phenomenon in which the coral expels it zooxanthellae and turns white (4) (10).

The great star coral is particularly vulnerable to disease (black band disease and white plague), while local threats include fisheries, invasive species, pollution, human development, tourism and recreation. Corals are particularly affected by the changing global climate, with rising sea temperatures, ocean acidification and mass coral bleaching events all contributing to significant declines in coral populations (1).

The great star coral is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which means that all trade in the species should be carefully monitored. The great star coral is also known from several Marine Protected Areas, including Florida Keys National Marine Sanctuary, Biscayne National Park, Dry Tortugas National Park, Buck Island Reef National Monument and Flower Garden Banks National Marine Sanctuary, as well as others in Belize and the Bahamas. In US waters, it is illegal to harvest corals for commercial purposes (1).

More research is needed on the taxonomy, population status, ecology and habitat of the great star coral and its resilience to major threats. New protected areas should be identified and established, while further research into coral disease is also required (1).

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk

Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.

Calcareous: containing free calcium carbonate, chalky.

Colonies: a group of organisms living together. Individuals in the group are not physiologically connected and may not be related, such as a colony of birds. Another meaning refers to organisms, such as bryozoans, which are composed of numerous genetically identical modules (also referred to as zooids or ‘individuals’), which are produced by budding and remain physiologically connected.

Photosynthesis: metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.

Photosynthetic: capable of photosynthesis, a metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.

Polyp: typically sedentary soft-bodied component of cnidaria, a group of simple aquatic animals including the sea anemones, corals and jellyfish. A polyp comprises a trunk that is fixed at the base, and a mouth that is placed at the opposite end of the trunk and is surrounded by tentacles.

Septa: in a coral, radial elements that project inwards from the corallite wall (the skeletal wall of an individual coral polyp).

Spawning: the production or depositing of large quantities of eggs in water.